Electrical submersible pumps for oil wells are typically driven by three-phase submersible AC electrical motors. Large submersible pump motors may be forty feet long and 7.25 inches in diameter. The motor has a stationary stator that is made up of a large number of discs or laminations stacked in the housing. Each lamination is a circular flat steel plate having a central opening through which the rotor extends. Also, each disc has a plurality of slots extending around the central opening for receiving windings.
A dielectric film lines each slot to provide a dielectric barrier between each disc and the windings that pass through the slots. The dielectric film must withstand high temperatures and voltages. One suitable type is a polyimide, however this type of insulation material does not melt or fuse to itself. It is installed in the slot by folding a long ribbon or strip of the material longitudinally with the edges overlapping.
While this insulation works well enough, because the edges overlap, an electrical leak path exists. Also, it would be desirable to reduce the thickness of the dielectric material.